1. Field of the Invention
This invention relates to a means for inhibiting the application of damaging axial forces to a rotary device. The invention relates more particularly to a grass cutting device having a rotating shaft and means for protecting a rotary motive means from damaging axial forces inadvertently applied to the shaft.
2. Description of the Prior Art
In various devices employing a prime mover having an output rotary shaft, axial forces are at times applied to the shaft which can have a damaging effect on the prime mover. This can occur for example with an electric motor which rotates a tool or cutter or the like. More particularly, in the field of consumer products wherein large production quantities of an appliance or device are manufactured, the cost factor is particularly important and efforts are generally taken to provide designs having desired operating characteristics and reliability yet at the lowest design cost achievable. In this regard, in various electrically operated devices as for example electrically operated lawn mowers or grass trimmer devices, it is desirable from a cost viewpoint to utilize electric motor means in which the supports for the motor are designed to handle rotary loads but are not specificially designed to sustain axial thrust or impact loads. While a significant cost saving can be achieved with this arrangement, the device is at times undesirably subjected to relatively strong axial impact forces which can have a damaging effect on the motor. Although thrust bearings may be provided to compensate for these loads which at times can be significant, the loads are random and from a cost viewpoint do not warrant the inclusion in the motor design of relatively expensive thrust bearings. This is the case for example with portable grass trimming devices which are generally held and manipulated by the user above the ground during the process of cutting and trimming the grass. The user will, at times, inadvertently impact a cutter support hub of the device with a rock or other structure in a manner which causes an axial thrust load which can have a damaging effect on the electric motor.